Compasses of various kinds are known in the state of the art and are used for orienteering, i.e. the practice of using a map and a compass to determine the route of travel. Commonly, those compasses comprise a base member and a vial assembly pivotally coupled to the base member. The vial assembly comprises a vial and an azimuth ring as well as a magnetized indicator member pivotally journaled in the vial. Moreover, an orienting marker is located in the vial. Commonly, the orienting marker is in form of an orienting arrow.
Generally, the magnetized indicator member is a needle pointing to magnetic north. However, the magnetic north is not equal to true north, i.e. the direction along the earth's surface to the geographic North Pole. This magnetic declination varies on the temporal and on the spatial scale. In general, topographic maps are drawn to true north. Hence, those maps intended for navigational purposes contain information on the size of the declination and of the angle of the declination. For instance, on the maps issued by the U.S. Geological Survey, a diagram is provided showing the relationship between true north and magnetic north.
For taking a bearing using a compass and a map, the orienting marker is “moved” by an angle accounting for the declination as given on the map. For instance, if the declination is 5° E, the orienting marker must lie 5° E of 0° N. For doing so, the vial has to be moved relative to the azimuth ring, as the orienting marker is part of the vial. Despite of the needle still pointing towards magnetic north, the azimuth ring and the bearings taken now represent true north bearings.
To account for the declination when using the compasses known in the state of the art, tools are often required to rotate the vial relative to the azimuth ring. Alternatively, the coupling between the vial and the azimuth ring is provided by power of a spring. Hence, one either needs a separate member or a complex construction which is prone to disadvantages e.g. caused by the entering of water or dirt to that can impede the movement of the declination setting mechanism.
The objective of the present invention is to provide a compass which facilitates to account for the declination.